This invention relates to a method for controlling the mold compression process in an injection molding machine. More particularly this invention relates to a method for controlling the pressure and velocity of compression in a compression process.
An injection molding machine utilizes a mold clamping process to compress molten resin which is molded in a cavity. In conventional type injection molded machines the compression process is controlled with a programmed control method wherein the values of pressure to be used for compression are programmed in accordance with positions of an injection plunger or screw mounted on the machine, or in accordance with a plurality of time intervals.
It is difficult in the conventional type injection molding machine to perform high accuracy molding such as is needed for thin plates or resin having high viscosity such as are used to produce articles such as recording discs, records etc. because the velocity of the moving die plate during compression is not kept constant. The velocity fluctuates due to changes in the temperature of the mold die and the pressurized oil. The changes in velocity of the moving die plate cause distortions in form from incomplete filling of the mold if the velocity is too low and cavities in the articles if the velocity is too high.